Asteroids pounding fractured Moon's upper crust

Nearly four billion years ago, the moon took a severe beating as a barrage of asteroids pelted its surface, carving out craters and opening deep fissures in its crust, scientists have revealed. Such sustained impacts increased the moon's porosity, opening up a network of large seams beneath the lunar surface during a period called the "Late Heavy Bombardment".

Scientists from Massachusetts Institute of Technology (MIT) have identified regions on the far side of the moon, called the lunar highlands, that may have been heavily bombarded particularly by small asteroids.

The impacts completely shattered the upper crust, leaving these regions essentially as fractured and porous as they could be.

"The evolution of the moon's porosity can give scientists clues to some of the earliest life-supporting processes taking place in the solar system," said Jason Soderblom, research scientist in MIT's department of earth, atmospheric and planetary sciences.

The researchers observed this effect in the upper layer of the crust a layer that scientists refer to as the megaregolith.

This layer is dominated by relatively small craters, measuring 30km or less in diameter.

In contrast, it appears that deeper layers of crust, that are affected by larger craters, are not quite as battered, and are less fractured and porous.

"The whole process of generating pore space within planetary crusts is critically important in understanding how water gets into the subsurface," Soderblom explained.

On Earth, scientists believe that life may have evolved somewhat in the subsurface.

"This is a primary mechanism to create subsurface pockets and void spaces, and really drives a lot of the rates at which these processes happen. The moon is a really ideal place to study this," the authors noted in the journal Geophysical Research Letters.

The team used data obtained by Nasa's Gravity Recovery and Interior Laboratory (GRAIL) twin spacecraft that orbited the moon throughout 2012, each measuring the push and pull of the other as an indicator of the moon's gravity.

Ultimately, tracing the moon's changing porosity may help scientists track the trajectory of the moon's impactors four billion years ago.